Lithium-ion secondary batteries are batteries with high output, so that they have come into wide use as power supplies not only for portable terminal devices, mobile communication apparatus, and the like, but also for electric cars, hybrid cars, and the like. More than 10 years have already passed since lithium-ion secondary batteries hit the market, and various attempts have been proposed to improve their characteristics. In general, a lithium-ion secondary battery comprises an electrode active material adapted to occlude and release lithium ions, positive and negative electrodes, and a liquid electrolyte, whereas various substances are used as the electrode active material.
In particular, as a positive electrode active material used for the positive electrode, lithium-containing transient metal oxides are used in general. Atypical example is lithium cobalt oxide (LiCoO2), where as Japanese Patent Application Laid-Open No. HEI 4-300158, Japanese Patent Application Laid-Open-No. HEI 4-106875, Japanese Patent Application Laid-Open No. HEI 4-267053, and U.S. Pat. No. 5,264,201, for example, disclose LiMnNiCo type complex oxides as a multiple metal oxide including a plurality of kinds of transient metal elements.